The couple were stabbed to death near the Queen Street Matalan store where they worked on 28 September 2016.

Saunders' barrister told London's Court of Appeal he had been mentally unwell.

Winston Roddick QC told the preliminary hearing Saunders suffered from an "adjustment disorder", which, if known at the time, would have allowed him to put forward a defence of diminished responsibility.

"A characteristic of adjustment disorder is that the sufferer will appear normal and indistinguishable from others," he told the judges.

Lady Justice Hallett said his appeal hearing should be listed as soon as a date is convenient, but no date has yet been set.

Saunders, of Castleton near Newport, bought knives and latex gloves in the days leading up to the double murder and searched Google for topics including "the easiest way to kill a person" and "how long do murderers serve in prison".

He was previously in a relationship with Miss Morgan for two years, but she ended it in July 2016.